Dual actuator storage device utilizing multiple disk zones

ABSTRACT

A recording surface of a magnetic disk is divided into first and second zones. A first head of a first actuator arm assembly reads from and/or writes to the first zone exclusively. A second head of a second actuator arm assembly reads from and/or writes to the second zone exclusively. The first and second head are capable of simultaneously reading from and writing to the recording surface.

SUMMARY

The present disclosure is directed to a dual actuator storage deviceutilizing multiple disk zones. In one embodiment, a recording surface ofa magnetic disk is divided into first and second zones. A first head ofa first actuator arm assembly reads from and/or writes to the first zoneexclusively. A second head of a second actuator arm assembly reads fromand/or writes to the second zone exclusively. The first and second headare capable of simultaneously reading from and writing to the recordingsurface.

These and other features and aspects of various embodiments may beunderstood in view of the following detailed discussion and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The discussion below makes reference to the following figures, whereinthe same reference number may be used to identify the similar/samecomponent in multiple figures.

FIG. 1 is a top view of a data storage device according to an exampleembodiment;

FIGS. 2 and 3 are block diagram showing tracks having different geometrythat may be used on the same recording medium according to an exampleembodiment;

FIG. 4 is a block diagram of a format for a recording medium accordingto an example embodiment;

FIG. 5 is a block diagram of a format for a recording medium accordingto another example embodiment;

FIG. 6 is a block diagram of a format for a recording medium accordingto another example embodiment;

FIG. 7 is a graph showing seek length vs. seek time for a hard driveaccording to an example embodiment;

FIG. 8 is a flowchart of a method according to an example embodiment;and

FIG. 9 is a block diagram of an apparatus according to an exampleembodiment.

DETAILED DESCRIPTION

The present disclosure generally relates to disk drive storage. Whilenewer technologies such as solid-state drives (SSD) are gainingpopularity due, e.g., to high speed and mechanical ruggedness, there arestill a number of applications where traditional magnetic disk storage,or hard disk drive (HDD), is preferable. The cost per unit of datastored for disk storage is much lower than in newer technologies such asSSD. For some applications, such as recording video, the combination oflow cost and good sequential read/write performance makes the HDD thebest option. Even in systems where an SSD is used, e.g., for theoperating system, an HDD is often added for user data storage.Accordingly, manufacturers still seek to improve HDD performance whilestill retaining cost advantages over other types of drives.

In order to improve sequential write performance of an HDD, a number ofschemes have been developed that allow two or more read/write heads toaccess the recording media in parallel. Parallelism allows for as muchas doubling sequential data rates, increases large block randominput-output-per-second (IOPS) by 20-50% over a single-stream drive, andreduces manufacturing test time. One way to achieve parallelism is touse two independent actuators that both actuators cover the samerecording area on a common spindle motor and disk pack.

In FIG. 1, a block diagram shows a data storage device 100 according toan example embodiment. The device 100 includes one or more magneticdisks 102 driven by a common spindle motor 104. Two arms 106, 108 thatrotate about separate pivots 110, 112 are driven by respective actuatormotors 114, 116. The actuator motors 114, 116 are also often referred toas voice coil motors (VCMs). The actuator motors 114, 116 cause the arms106, 108 to change radial locations (tracks) in response to inputs froma servo controller. The pivots 110, 112 are located on opposite sides ofthe disk 102 in this example. In the following disclosure, the arms 106,108 and actuator motors 114, 116 are collectively referred to asactuator assemblies. More than two actuator assemblies can be used,albeit with a corresponding increase in size and weight of the device.

The arms 106, 108 each have a read/write head (also referred to as aslider, reader, writer, etc.) at the distal end. Because both surfacesof the disk(s) 102 may be used for data storage, there may be arms overboth surfaces of the disk 102 each with one read/write head for eachdisk surface. Because the illustrated device 100 has two independentarms 106, 108, each read/write head can simultaneously read from orwrite to different parts of the same disk surface, or different surfacesof the same or different disks. The reading/writing can be coordinated,e.g., each read/write head handling part of the same data stream. Thereading/writing can also be independent, e.g., each read/write headhandling different data streams, e.g., each associated with differenthost requests.

An independent actuator system as shown in FIG. 1 is less complex thanto other proposed parallelism designs, such as one using a single VCMwith micro-actuators to control heads and simultaneously transfer dataon the opposite sides of a disk. The system shown in FIG. 1 can utilizeexisting servo control systems to control the separate arms 106, 108.The system can utilize conventional (e.g., perpendicular) read/writeheads, and can also be adapted to newer technologies, such asheat-assisted magnetic recording (HAMR).

If the read/write heads in a configuration as shown in FIG. 1 areconfigured to read and write the same tracks on the same surface, thesystem will have to account for matching the read/write heads to thetracks. Due to manufacturing tolerances, each read/write head will haveslightly different characteristics, such as write width, magnetic fieldstrength, reader resolution, reader width, reader-to-writer offset, etc.In a conventional drive where only one head writes to a surface, trackgeometry can be customized to account for the characteristics of thehead writing to each surface. When using two heads on the same surface,the selected track geometry needs to take into account differencesbetween the heads.

In FIGS. 2 and 3, block diagram shows tracks 200, 300 having differentgeometry that may be used on the same data storage device. The trackcenter-to-center distance 202, or track pitch, in FIG. 2 is smaller thanthe corresponding distance 302 in FIG. 3. This means that theconfiguration shown in FIG. 2 has higher track density, often expressedin tracks per inch (TPI). The distance 204 between bit transitions inFIG. 2 is larger than corresponding distance 304 in FIG. 3. This meansthat the configuration in FIG. 3 has higher linear bit density, oftenexpressed in bits per inch (BPI). Note that for actual data there maynot be a magnetic transition for every vertical line shown in FIGS. 2and 3. Generally, the lines indicate a minimum distance betweentransitions, and in cases where adjacent bits are the same, a bitboundary may be inferred, e.g., by a clock in the read or write channel.

Generally, the TPI and BPI and suitable for particular heads may bedetermined in the factory after manufacture and testing of the head. Forexample, the heads can be tested and sorted based on various criteriathat determine a maximum TPI and BPI for each head. When used in aconfiguration where different read/write heads read/write the sametracks on the same surface, the heads will need to read and write at thesame TPI and BPI. In order to do this, the lowest TPI and BPI of bothheads will need to be selected. However, this provides the minimalamount of areal density (ADC), because the ADC is generally a functionof the TPI times the BPI.

The dual actuator configuration with both heads reading the same trackscan increase the factory test time due to the need to have the heads onthe same surface be able to reliably read the same tracks. For example,this may involve testing the combination of writer and reader of bothheads on each radial zone of the disk for channel optimization,determining bit-aspect ratio (e.g., TPI and BPI as shown in FIGS. 2 and3), determining/minimizing adjacent track interference (ATI), etc. Inaddition, the servo control system will store data tables for correctionof repeatable runout (RRO) and skew, and these tables will be duplicatedfor both heads. There may also be an ADC penalty due to head alignment.For example, there will be an angle between the track written by onehead's writer and read by the other head's reader. Track characteristicssuch as TPI may need to be increased to account for the these angles.

In embodiments discussed below, a data storage device 100 as shown inFIG. 1 divides the disk surface into zones, each zone dedicated to oneread/write head. The zones may be contiguous regions, or include groupsof tracks interleaved with each other, each group belonging to adifferent zone. Each read/write head reads/writes exclusively to itstarget zone, thereby allowing the track geometry in the zones to betailored to the characteristics of the head.

In FIG. 4, a diagram shows a format for a recording medium 400 accordingto an example embodiment. In this example, odd tracks 402 are written ata first track pitch 403 and even tracks 404 are written at a secondtrack pitch 405. The even and odd tracks 402, 404 have correspondinglydifferent track widths, e.g., the even tracks 404 being wider in thisexample. A first head 406 on one actuator assembly writes and reads allodd tracks 402 and a second head 408 on another actuator assembly writesand reads all even tracks 404. The BPI and TPI between odd and eventracks are totally separated. The odd track BPI and TPI are picked basedon the head 406 on one actuator assembly. The even track BPI and TPI arepicked based on the corresponding head 408 on the other actuatorassembly. The effective BPI and TPI are the average value of two heads,which maximizes ADC given the different capabilities of the heads 406,408.

In FIG. 5, a diagram shows a format for a recording medium 500 accordingto another example embodiment. In this arrangement, the recording mediumis divided into a first zone 502 and a second zone 504. Zone 502 has twogroups 502 a-b of multiple tracks, and zone 504 has two groups 504-ab ofmultiple tracks. These groups 502 a-b, 504 a-b may correspond to servozones that utilize different numbers of sectors per track to maintainapproximately equal sector size between inner and outer diameter of thedisk 500. For purposes of simplicity, a total of two groups of tracksfor each zone is shown in FIG. 5, however the recording medium 500 maybe divided, evenly or unevenly, into any number of groups, and thosegroups be assigned in any order to the two zones (or more zones if moreheads are used).

The head on first actuator assembly 506 exclusively writes and reads alltracks in the first zone 502 and head on another actuator assembly 508exclusively writes and reads all tracks in the second zone 504. Thefirst and second zones 502, 504 have BPI and TPI optimized for theirrespective read/write heads. The system of alternating group design maybe more simple to implement compared to that of alternating tracks sinceeach group within zones 502, 504 may only have one BPI and one TPI. Thismay also reduce the factory test time and firmware complexity.

Generally, the embodiments in FIGS. 4 and 5 are both examples first andsecond groups of tracks arranged such that the first groups of tracksare interleaved between the second groups of tracks. A subset of thegroups is assigned to one zone and the remaining groups are assigned tothe other zone. The case in FIG. 4 represents a configuration where eachgroup is a single track. The case in FIG. 5 represents a configurationwhere each group is greater than one track. In the latter case, thegroups can be equal or different sizes. For example, in FIG. 5 theindividual groups 502 a-b that make up zone 502 may have the same amountof storage space but different numbers of tracks, or vice versa. Thegroups 504 a-b that make up zone 504 may have the same or differentarrangement.

In FIG. 6, a diagram shows a format for a recording medium 600 accordingto another example embodiment. The recording medium surface is separatedinto two regions 602, 604, which are inner and outer annuli of the disk600. Region 602 is an outer radius area for the head on a first actuatorassembly 606. Region 606 is an inner radius area for the head on theother actuator assembly 608. The first and second regions 602, 604 haveBPI and TPI optimized for their respective read/write heads. Thisarrangement may improve random IOPS and ADC.

In alternate embodiments the allocation of zones to heads may bedifferent when reading versus writing. For example, in FIGS. 4 and 5,the head on one actuator may be used for writing a recording zone, whilethe head from the other actuator may be used for reading that zone. Inanother embodiment, certain zones may only be written by the recordinghead on one actuator, but may be readable by the recording heads on bothof the actuators. The opposite is also possible, e.g., certain zones maybe written by recording heads from both actuators, but may be read bythe recording head from only one of the actuators.

In FIG. 7, a graph shows the seek length vs. seek time for an examplehard drive. The seek time increases monotonically with seek length. Ittakes about 7.2 ms when seeks from the minimum track to maximum track orvise verse. In the arrangement of FIG. 6, the seek between innermost andoutermost portions of regions 602 and 604 is half of what it would be ifthe dedicated regions were spread across the disk. By shortening theseek length to half, the average seek time is reduced and random IOPS isimproved.

The outer/inner design configuration shown in FIG. 6 could also improveADC by reducing skew angle and data rate effect. Note that each actuatorassembly 606, 608 has to track only half the angle than if the armstraversed the entire surface of the medium 600. As such the heads can bedesigned for a reduced skew angle at the maximum skew locations, whichare typically at the inner and outer edges of the annuli 602, 604. Theformat and reduction in skew angle by half would reduce track pitch andimprove adjacent track interface performance. It may also benefit thehead-to-disk interface, such as ABS design optimization for skew angle.Furthermore, since the data rate at the inner radius area 604 is lowerthan that of the outer radius area 602, each head can be optimizedseparately. For example, a high data rate/low ADC head can be used forthe outer radius area 602, and low data rate/high ADC head can be usedfor the inner radius area 604. In such a case one high-data rate headand one low-data rate head can be used, which can achieve higher ADCthan two high-data rate heads.

It should be noted that the latency in the random write/read may belonger in these configurations than in the configurations where bothread/write heads can access all the tracks on the surface. In the designshown in FIGS. 4-6, the average latency is half of the revolution, sameas in conventional magnetic recording. In a configuration where bothread/write heads can access all the tracks on the surface, the averagelatency is only ¼ of the revolution. For a 5400 RPM drive, a ½ tracklatency is about 6 ms, compared to 3 ms for a ¼ track latency. However,this increase in latency can be offset, at least in the configurationshown in FIG. 6, by halving the seek length, as illustrated in FIG. 7.

In FIG. 8, a flowchart shows a method according to an exampleembodiment. The method involves dividing 800 a recording surface of amagnetic disk into first and second zones. The first zone is read fromand written to 801 exclusively via a first head of a first actuator armassembly. The second zone is read from and written to 802 exclusivelyvia a second head of a second actuator arm assembly. As indicated by theparallel orientation of the blocks 801, 802, the first and second headare capable of simultaneously reading from or writing to the magneticdisk. This could involve reading/writing a common data stream togetherthat is interleaved between zones. In other embodiments, the first andsecond heads could be servicing different host requests at the sametime, the requests affecting independent data stored in different zones.

In FIG. 9, a block diagram illustrates an apparatus 900 according to anexample embodiment. The apparatus 900 includes circuitry 902 thatfacilitates writing data to and reading data from a magnetic disk 910.The circuitry 902 includes a system controller 904 that overseesoperations of the apparatus 900. The system controller 904 may include agenerally purpose central processing unit, application specificintegrated circuit, multi-function chipset, etc. Generally, the systemcontroller 904 receives commands from a host 906 via a host interface907. The host commands may include requests to load, store, and verifydata that is targeted for the disk 910.

The apparatus includes first and second actuator assemblies 914, 916that each include respective VCMs 914 a, 916 a, arms 914 b, 916 b, andread/write heads 914 c, 916 c. The first and second read/write head 914c, 916 c exclusively write to and read from the first and second zones910 a-b at a common surface of the disk 910. The zones 910 a-b may beconfigured with different track pitches and/or different linear bitdensities, e.g., that are optimized for the respective heads 914 c, 916c.

The system controller 904 utilizes instructions that define the zonesfor all surfaces of all of the disks 910, and cause the heads 914 c, 916c to write exclusively to the respective zones 910 a-b. This isrepresented by zone management component 905. Servo controllers 916cause independent movement of the first and second actuator assemblies914, 916, e.g., for seeking to and tracking on different tracks withinthe respective zones. One or more read write channels 908 allowsimultaneous reading and writing from the different read/write heads 914c, 916 c. The read/write channel 908 may be coupled to the read writeheads 914 c, 916 c via interface circuitry 912 such as preamplifiers,digital-to-analog converters, analog-to-digital converters, filters,etc.

The various embodiments described above may be implemented usingcircuitry, firmware, and/or software modules that interact to provideparticular results. One of skill in the arts can readily implement suchdescribed functionality, either at a modular level or as a whole, usingknowledge generally known in the art. For example, the flowcharts andcontrol diagrams illustrated herein may be used to createcomputer-readable instructions/code for execution by a processor. Suchinstructions may be stored on a non-transitory computer-readable mediumand transferred to the processor for execution as is known in the art.The structures and procedures shown above are only a representativeexample of embodiments that can be used to provide the functionsdescribed hereinabove.

The foregoing description of the example embodiments has been presentedfor the purposes of illustration and description. It is not intended tobe exhaustive or to limit the embodiments to the precise form disclosed.Many modifications and variations are possible in light of the aboveteaching. Any or all features of the disclosed embodiments can beapplied individually or in any combination are not meant to be limiting,but purely illustrative. It is intended that the scope of the inventionbe limited not with this detailed description, but rather determined bythe claims appended hereto.

What is claimed is:
 1. An apparatus, comprising: a first actuatorassembly comprising a first head configured to write to a recordingsurface of a magnetic disk; a second actuator assembly comprising asecond head configured to write to the recording surface simultaneouslywith the first head; and a controller coupled to the first and secondactuator assemblies; the controller configured to: divide the recordingsurface into first and second zones; and cause the first and secondheads to write exclusively to the first and second zones respectively.2. The apparatus of claim 1, wherein the first and second zones compriserespective two or more first groups of track and two or more secondgroups of tracks, the first group of tracks interleaved between thesecond group of tracks.
 3. The apparatus of claim 2, wherein the groupseach comprise a single track.
 4. The apparatus of claim 2, wherein thegroups each correspond to a different servo zone of the magnetic disk.5. The apparatus of claim 1, wherein the first and second zones compriserespective inner and outer annuli of the recording surface.
 6. Theapparatus of claim 5, wherein the first head and the second head areoptimized for reduced skew angles in the inner and outer annuli.
 7. Theapparatus of claim 5, wherein the outer annuli is configured for highdata rate/low areal density and the inner annuli is configured for lowdata rate/high areal density.
 8. The apparatus of claim 1, wherein thefirst and second zones utilize at least one of different track pitchesand different linear bit densities, the first and second heads beingoptimized for the respective different track pitches and differentlinear bit densities.
 9. The apparatus of claim 1, wherein thecontroller further causes the first and second heads to read exclusivelyfrom the first and second zones respectively.
 10. A method, comprising:dividing a recording surface of a magnetic disk into first and secondzones; reading from and writing to the first zone exclusively via afirst head of a first actuator arm assembly; reading from and writing tothe second zone exclusively via a second head of a second actuator armassembly, the first and second head capable of simultaneously readingfrom and writing to the recording surface.
 11. The method of claim 10,wherein the first and second zones comprise respective two or more firstgroups of track and two or more second groups of tracks, the first groupof tracks interleaved between the second group of tracks.
 12. The methodof claim 10, wherein the first and second zones comprise respectiveinner and outer annuli of the recording surface.
 13. The method of claim12, further comprising optimizing the first head and the second head forreduced skew angles in the inner and outer annuli.
 14. The method ofclaim 12, further comprising configuring the outer annuli for high datarate/low areal density and configuring the inner annuli for low datarate/high areal density.
 15. The method of claim 10, further comprisingsetting different track pitches and different linear bit densities forthe first and second zones, the different track pitches and thedifferent linear bit densities selected based on capabilities of therespective first and second heads.
 16. An apparatus comprising: amagnetic disk comprising a recording surface divided into first andsecond zones; a first actuator arm assembly comprising a first headconfigured to exclusively read from first zone; and a second actuatorassembly comprising a second head configured to exclusively read fromthe second zone, the first and second heads capable of simultaneouslyreading from the recording surface.
 17. The apparatus of claim 16wherein the first and second heads are further configured to exclusivelywrite to the respective first and second zones.
 18. The apparatus ofclaim 16, wherein the first and second zones comprise respective two ormore first groups of track and two or more second groups of tracks, thefirst groups of tracks interleaved between the second groups of tracks.19. The apparatus of claim 16, wherein the first and second zonescomprise respective inner and outer annuli of the recording surface. 20.The apparatus of claim 16, wherein the first head is configured to readfrom the first zone at a first track pitch and first linear bit densityand the second head is configured to read from the second zone at asecond track pitch and second linear bit density.